I'm trying to recall the name of a steampunk novel. Some time in the future, most cities are gone, with remaining cities being giant platforms on legs. these cities survive by chasing down smaller cities and then "eating" them (taking the inhabitants as prisoners or new members, and taking the old city and using it as scrap or new material). This is in the future because they still talk about finding old "seedys" (CD's) that seem decorative.
That sounds like Mortal Engines and its' sequels by Philip Reeve.
Is it Mortal Engines Quartet by Philip Reeve? This includes:
Mortal Engines (2001), Predator's Gold (2003), Infernal Devices (2005), and A Darkling Plain (2006).
The Quartet is set in the distant future, in an age known as the Traction Era. Earth has been reduced to wasteland by a devastating conflict, known as the Sixty Minute War. Nations no longer exist, except in the lands of the Anti-Traction League; Traction Cities - entire cities mounted on caterpillar tracks for mobility - are fiercely independent city-states, using giant jaws to devour one another for resources.